The objective is evaluation of of intravascular, tissue, and surface oxygen, carbon dioxide, and pH sensors. The proposal will involve selection on the basis of sensor drift, linearity, and response time obtained by bench controlled determinations. Clinical feasibility studies will be done on rabbits to evaluate sensor reliability. Long term reliability will then be evaluated in monkeys. Clinical tests will then be done in neonates with respiratory distress syndrome, pediatric patients in need of blood gas monitoring in the intensive care units, and post-cardiac surgery patients and patients requiring extrocorporeal membrane oxygenation.